The present invention relates to improvements in chain saws. In particular, the invention relates to a safety interlock arrangement for the chain saw throttle actuator to prevent, in certain circumstances, movement of the actuator, under the influences of the actuator biasing systems and pressure exerted on the actuator by an operator of the chain saw.
Although various other chain saw safety devices have been proposed, previous arrangements have had different structures and/or different functions. Thus, for example, Irgens, U.S. Pat. No. 3,361,165 discloses a lever on the forward handle bar of a chain saw that is operable, through intermediate flexible cables, to control the operation of a safety clutch (which prevents operation of the chain saw when it is not properly held by the front handlebar) and of the throttle. This throttle control is thus a "two handed" system requiring a somewhat elaborate, and potentially cumbersome, linkage. In Johannson, U.S. Pat. No. 3,785,465, a safety device causes disengagement of a driving portion of a chain saw clutch when a safety grip is released. The safety grip is provided on the chain saw handgrip, but operates only by electrical connection with an electromagnet and, additionally, operates only upon a chain saw clutch rather than directly upon the throttle actuator.
Of course, throttle control devices, and other safety mechanisms, have been known in other fields for some time. The problems being solved in those fields, as well as the structures used to solve them are, of course, typically quite different from the environment of the present invention. Illustrative of such situations are Thorner, U.S. Pat. Nos. 2,917,142 and 3,168,933, each of which is directed to a throttle control mechanism for use in a motor vehicle. In the firearms category, mention can be made of Randall, U.S. Pat. No. 1,509,257 which discloses an arrangement preventing depression of the weapon's trigger unless the weapon is properly gripped by the user. While the illustrative embodiment in the Randall patent is that of a rifle, it is well known that arrangements have been provided on pistols.